The use of fossil fuel as the combustible fuel in gas turbine engines results in the combustion products of carbon monoxide, carbon dioxide, water vapor, smoke and particulates, unburned hydrocarbons, nitrogen oxides and sulfur oxides. Of these above products, carbon dioxide and water vapor are considered normal and unobjectionable. In most applications, governmental imposed regulations are restricting the amount of pollutants being emitted in the exhaust gases.
In the past the majority of the products of combustion have been controlled through design modifications and fuel selection. For example, at the present time smoke has normally been controlled by design modifications in the combustor, particulates are normally controlled by traps and filters, and sulfur oxides are normally controlled by the selection of fuels being low in total sulfur. This leaves carbon monoxide, unburned hydrocarbons and nitrogen oxides as the emissions of primary concern in the exhaust gases being emitted from the gas turbine engine.
Oxides of nitrogen are produced in two ways in conventional combustion systems. For example, oxides of nitrogen are formed at high temperatures within the combustion zone by the direct combination of atmospheric nitrogen and oxygen and by the presence of organic nitrogen in the fuel. The rates with which nitrogen oxides form depend upon the flame temperature and, consequently, a small reduction in flame temperature can result in a large reduction in the nitrogen oxides.
Past and some present systems providing means for reducing the maximum temperature in the combustion zone of a gas turbine combustor have included schemes for introducing more air at the primary combustion zone, recirculating cooled exhaust products into the combustion zone and injecting water spray into the combustion zone. An example of such a system is disclosed in U.S. Pat. No. 4,733,527 issued on Mar. 29, 1988 to Harry A. Kidd. The method and apparatus disclosed therein automatically maintains the NOx emissions at a substantially constant level during all ambient conditions and for no load to full load fuel flows. The water/fuel ratio is calculated for a substantially constant level of NOx emissions at the given operating conditions and, knowing the actual fuel flow to the gas turbine, a signal is generated representing the water metering valve position necessary to inject the proper water flow into the combustor to achieve the desired water/fuel ratio.
An injector nozzle used with a water injection system is disclosed in U.S. Pat. No. 4,600,151 issued on Jul. 15, 1986 to Jerome R. Bradley. The injector nozzle disclosed includes an annular shroud means operatively associated with a plurality of sleeve means one inside the other in spaced apart relation. The sleeve means form a liquid fuel-receiving chamber, a water or auxiliary fuel-receiving chamber inside the liquid fuel-receiving chamber for discharging water or auxiliary fuel in addition or alternatively to the liquid fuel, an inner air-receiving chamber for receiving and directing compressor discharge air into the fuel spray cone and/or water or auxiliary fuel to mix therewith from the chamber for receiving and directing other compressor discharge air into the fuel spray cone and/or water or auxiliary fuel from the outside for mixing purposes.
Another example of a fuel injector for a gas turbine engine is disclosed in U.S. Pat. No. 4,463,568 issued on Aug. 7, 1984 to Jeffrey D. Willis et. al. In this patent, a dual fuel injector is arranged to maintain pre-determined air fuel ratios in adjacent upstream and downstream opposite handed vortices and to reduce the deposition of carbon on the injector. The injector comprises a central duct, a deflecting member, a first radially directed outlet, a shroud which defines an annular duct, and a second radially directed outlet. The ducts receive a supply of compressed air, the central duct receives gaseous fuel from an annular nozzle and the annular duct receives liquid fuel from a set of nozzles. When the injector is operating on liquid fuel, the fuel and air mixture issues from the second outlet and compressed air flows from the first outlet and prevents migration of fuel between the two vortices, thereby maintaining a rich air fuel ratio in the upstream vortex which reduces the emissions of NOx. Also, the flow of air from the first outlet reduces the deposition of carbon from the liquid fuels on the deflecting member.
Another fuel injector is disclosed in U.S. Pat. No. 4,327,547 issued May 4, 1982 to Eric Hughes et. al. The fuel injector includes means for water injection to reduce NOx emissions and an outer annular gas fuel duct with a venturi section with air purge holes to prevent liquid fuel entering the gas duct. Further included is an inner annular liquid fuel duct having inlets for water and liquid fuel and through which compressor air flows. The inner annular duct terminates in a nozzle, and a central flow passage through which compressed air also flows, terminating in a main diffuser having an inner secondary diffuser. The surfaces of both diffusers are arranged so that their surfaces are washed by the compressed air to reduce or prevent the accretion of carbon to the injector, the diffusers in effect forming a hollow pintle.
Another combustor apparatus for use with a gas turbine engine is disclosed in U.S. Pat. No. 3,906,718 issued on Sep. 23, 1975 to Robert D. Wood. In this patent, a combustion chamber for a gas turbine engine which has staged combustion in two toroidal vortices of opposite hand arranged one upstream of the other is disclosed. A burner delivers air/fuel mixture in a radial direction to support the vortices and the burner has a convergent outlet for the air/fuel mixture.
The above system and nozzles used therewith are examples of attempts to reduce the emissions of oxides of nitrogen. Many of the attempts have resulted in additional expensive components. For example, the Kidd concept requires an additional means for injecting water into the combustion chamber which includes a water source, a control valve, a controlling and monitoring system and a device for injecting water into the combustion chamber.